Dark and luminous matter in the outer halos of elliptical galaxies

点击翻译按钮获取中文摘要

Much of the fossil record of elliptical galaxy formation is hidden at large radii, where dynamical times are long, dark matter dominates, and most of the angular momentum is expected to reside. The only tracers for studying stellar kinematics beyond a few effective radii are planetary nebulae (PNe). Results from a survey of PN kinematics in the outer halos of elliptical galaxies have revealed an unexplained dichotomy in their dynamics, which is not apparent from photometry alone. Dynamical modeling has also shown that several of these systems either contain little dark matter within five effective radii, or that their stellar halos are characterized by extreme radial orbit anisotropy. By contrast, modeling of X-ray bright systems is revealing massive and dense dark matter halos, and a strongly radially biassed outer distribution of stars. In order to understand better what lies behind these results, we propose to construct dynamical models for a well-chosen sample of both X-ray bright and X-ray faint ellipticals. The goal of the project is to determine the angular momentum content, orbital structure, and dark matter content of ellipticals as a function of luminosity and environment, and thereby obtain the necessary information for distinguishing between the different merger processes at work in the formation of elliptical galaxies.